About Opinions
Don’t take anyone’s word as authoritative – on anything. It’s all just opinion. There are more informed opinions and less informed opinions, on a continuous scale, but there are no authorities.
I don’t tend to rate very highly the opinions of those who claim that two plus two is five, or that the Earth is flat.
“Scientists say” doesn’t mean they’re necessarily right. You might rate their opinions more highly than those of an astrologer, a politician or an economist, but you should still remember that they’re just opinions. Scientists often disagree with each other, and even when they agree, they might be wrong. (Although if a huge majority of scientists agree, as on anthropogenic global warming, they're most probably not wrong – I wouldn't have that confidence about the opinion of a majority, however large, of economists or politicians.)
I don’t tend to rate very highly the opinions of those who claim to be authorities, either. Nor do I rate very highly the opinions of those who claim to be experts – unless they are also acknowledged to be experts by others whose opinion I’ve already assessed as reasonably reliable.
Your opinions are your own. You can use other people’s opinions to help you form them, but that process should take into account your estimate of the reliability of the opinions of the people whose opinions you’re considering – and no-one is 100% reliable, not even within their own specialization. Not even me.
For what it’s worth, my opinion is that one should be particularly suspicious of the stated opinions of anyone with a vested interest – not forgetting that some people’s vested interest may not be obvious. A vested interest can be something as simple as having taken a position for some reason, such as possibly having accepted some “authority’s” opinion, and then not being willing to admit that one was wrong. But financial vested interests are generally the most deviously hidden and most assiduously promoted.
See also Rationality, Science, Pseudoscience & Policy.